As a drive source for driving a wiper member, a wiper motor is used in a rear wiper device for wiping a rear window glass mounted on a vehicle such as an automobile. The wiper motor has an electric motor such as a brushed motor and rotatably supported one end to an axial direction of a motor shaft supported by a yoke. A speed reduction mechanism comprising a worm rotated by the motor shaft and a worm wheel meshing with the worm is contained inside a gear case mounted to the yoke. The speed of rotation of the motor shaft is reduced by the speed reduction mechanism and transmitting the rotation to the worm wheel. A motion conversion mechanism converting a rotational motion of the worm wheel into a swinging motion and transmitting the swinging motion to the output shaft is contained in a gear case. The wiper member attached to a distal end of the output shaft is swung back and forth within a predetermined angular range.
Such wiper motors are described, for example, in JP 2006-151092 and JP2006-94693. As a wiper motor, there are a narrow-angle type (link type) with a narrow range of swing of the wiper member and a wide-angle type (differential gear) with a wide range of swing of the wiper member. The motion conversion mechanism mounted on the wiper motor of the narrow-angle type has a pivoting lever fixed to a proximal end of the output shaft, and a connecting rod converting the rotary motion of the worm wheel into the swinging motion and transmitting the swinging motion to the pivoting lever. The connecting rod is rotatably connected to the worm wheel at a position deviating radially from an axial center of the worm wheel and another end of the connecting rod is rotatable connected to the pivoting lever.
On the other hand, the motion conversion mechanism mounted on the wiper motor of the wide-angle type has a pinion gear fixed to the proximal end of the output shaft and a motion conversion member converting the rotary motion of the worm wheel into the swinging motion and transmitting the swinging motion to the pinion gear. One end of the motion conversion member is rotatably connected to the worm wheel at a position deviating radially from an axial center of the worm wheel and another end is a sector gear portion meshing with the pinion gear. A retaining plate swingably connecting the output shaft and a gear shaft set at an axial center of the sector gear portion is set up and retains meshing of the pinion gear and the sector gear portion.